1. Field of the Invention
This invention relates to a suspension control system for a motor vehicle which allows a person to drive the motor vehicle with great comfort and with high stability.
2. Prior Art
In general, the comfort which one may feel while driving a motor vehicle (hereinafter referred to as "vehicle driving comfort") can be improved by decreasing the suspension damping force, while the stability in operation of the motor vehicle (hereinafter referred to as "vehicle driving stability") can be enhanced by increasing it. However, in this connection, it should be noted that if the damping force is set to a relatively low value, then the vehicle driving comfortableness is improved, but the vehicle driving stability is lowered; whereas if it is set to a relatively high value, then the vehicle driving stability is improved, but the vehicle driving comfort is lowered.
In order to overcome the above-described difficulties, a suspension control system has been proposed in the art which operates as follows (Japanese Utility Patent Application (OPI) No. 114708/1980 (the term "OPI" as used herein means an "unexamined published application")): When a motor vehicle travels at low speed, the vehicle driving comfortableness takes precedence over the vehicle driving stability; that is, the damping force is set to a low value; and when it travels at high speed, the damping force is switched over to a high value thereby to improve the vehicle driving stability.
However, it should be noted that the conventional suspension control system suffers from the following difficulties: That is, it is so designed that, when the motor vehicle is traveling at a high speed which is higher than a predetermined value, in order to enhance the vehicle driving stability the damping force is set to a relatively high value at the sacrifice of the riding comfort. Hence, with the conventional suspension control system, the motor vehicle may bound intermittently at the positions of road defects such as the seams of road surfaces; that is, the vehicle driving comfort is worsened in such a case.